> But that is exactly the point.
>
> The albedo of rocky planets is lower than the gas giants, Earth's for
> example is roughly 0.4. Mercury is only 0.12.
>
> But even if you assume an albedo of 1, i.e. the planet is as bright as the
> star it revolves around, (which is absurd at best you would consider an
> albedo of 0.5) there is no way that the apparent magnitude of an object
the
> size of Neptune is within the resolution of naked eye 50 light years away.
>
> And, since albedo is the ratio of light radiation hitting the surface
> divided by what is reflected. For the planets' absolute magnitude to even
> approach the stars absolute magnitude, it would have to be very close to
the
> star, and that alone would make it indistinguishable from the star itself
at
> that distance.

Very close indeed! If Neptune were only 10^6 km from the sun (absurdly
close) it would still receive just ~10^-4
of the sun's radiation & thus even with an albedo of 1 would be 10
magnitudes fainter than the sun.